The present invention is related to an image scanner, and more particularly to an image scanner which includes means for correcting the scanning results so as to have a better scanning quality. The present invention is also related to a method for improving scanning quality of an image scanner.
Nowadays, an image scanner has gradually become a standard peripheral equipment of a personal computer. Therefore, scanner manufacturers have been trying their best to improve the scanning quality, for example, to compensate brightness, chrominance, etc., and/or correct scanning line errors. On the other hand, high scanning speed is also a criterion of an exquisite image scanner.
In order to enhance the scanning speed of an image scanner, several devices and methods have been proposed in prior art. For example, please refer to FIG. 1 which schematically shows home-sensor means for speeding up the movement of an image pickup module 11 from a standby line N to a scan start line M, i.e. a document reference line. In this case, it is assumed that the image pickup module 11 reaches the scan start line M after moving a distance D from the standby line N along the arrow direction. In other words, the image pickup module 11 directly moves a pre-determined distance, rather than moves pixel by pixel to detect the presence of a document, and then starts scanning. Therefore, the movement of the image pickup module 11 from the standby line N to the scan start line M is fast.
However, there are likely to be defects resulting from errors of various parts and/or assembling inaccuracy in this home sensor means. For example, if the image pickup module 11 is inaccurately installed at a position lower than a predetermined one while assembling, i.e. the standby line is lowered, the actual scan start line M1 will be accordingly lower than the document reference line M after the same distance D of movement, referring to the dotted lines and the dotted arrow in FIG. 1. Therefore, the top portion 13 of the document 12 will be missed out in the scanning operation.
On the other hand, when the image pickup module 11 reaches the scan start line M, the nth pixel unit of a CCD of the image pickup module 11 generally serves as the start point of the same scanning line, and the nth pixel unit and the pixel units thereafter are used to simultaneously pick up the image of the document line by line. If the image pickup module 11 slightly deflects from its pre-determined path owing to an assembling defect, the same distance D of movement will make the image pickup module 11 reach another line M2 rather than the pre-determined scan start line M, referring to the dotted line and the dotted arrow of FIG. 2, so that the nth pixel unit of the CCD will be a little shifted, and the scanning of a left portion 14 of the document might be missed out. In addition, the scanning lines will slant.
Another conventional means is proposed to avoid the missing of document data. Please refer to FIG. 3 which schematically shows means for precisely determining a scan start point in an image scanner. On the scanning platform of this image scanner, a black region 21 is provided in front of a scan start line R where a front edge of a document 22 to be scanned is positioned. In this case, the image pickup module (not shown) quickly moves toward the black region 21, and then slowly passes through the black region 21 after reaches the black region 21 to detect the disappearance of the black color. When the detected black color disappears, the image pickup module keeps on moving and begins to measure a distance Q along the arrow direction. It is assumed that the scan start line R is reached after the image pickup module moves the distance Q from the reference point P. By this way, the downshift error resulting from the downshift installation of the image pickup module, as shown in FIG. 1, can be avoided because the predetermined distance Q is measured from the lower edge of the black region, i.e. the reference point P, rather than from the standby line of the image pickup module. Nevertheless, the defect of the conventional scanner indicated in FIG. 3 still exists in this means, and is not resolved.
Therefore, an object of the present invention is to provide an image scanner, which can use single means to simultaneously adjust various scanning results to improve scanning quality.
Another object of the present invention is to provide a method for improving scanning quality of an image scanner by easily and conveniently performing color calibration, and detection and correction of a deflection rate and/or an amplification error.
A first aspect of the present invention is directed to an image scanner. The image scanner includes a scanning platform for placing thereon an object to be scanned, which is marked thereon a document line for positioning a front edge of the object, a first color block located in front of the document line along a specific direction, and a second color block located in front of the document line along the specific direction and having an interface with the first color block; and the image scanner also includes a photo-signal processing device passing by the scanning platform from a home position along the specific direction, and performing a scanning operation from a scan start point behind the first and the second color blocks to read image data of the object, and converting the image data of the object into digital data for further processing. According to this aspect of the present invention, the interface of the first and the second color blocks includes a first reference point and a second reference point whose coordinates are detected according to color changes therearound, a shift from the first reference point to the scan start point is of a predetermined vector which can be used together with the coordinate of the first reference point for determining a position of the scan start point, and a distance between the first and the second reference points is of a constant value which can be used together with the coordinates of the first and the second reference points for determining a deflection rate of a scan track and an amplification error of a scan result.
In addition to the purposes of accurate scan start point, deflection correction and amplification adjustment, the first and the second color blocks can also be provided for color calibrations of the scan result. For example, if the two color blocks are formed of regions of standard white and standard black, respectively, calibrations of a light and a dark responses can be performed.
In a preferred embodiment, the first color block is enclosed within the second color block, and the first and the second color blocks are formed of regions of standard white and standard black, respectively, so that the. photo-signal processing device sequentially passes by the standard black region, the standard white region and the standard black region to perform color calibrations and error detection before the scanning operation starts. Alternatively, the first color block can be a standard black region and the second color block can be a standard white region so that the sequence the photo-signal processing device passes by is first the standard white region, next the standard black region and then the standard white region, and the same purposes can be achieved.
It is to be noted that the first constant value should be set adequately so as to maximize the overall scan speed while avoiding the scanning operation starting after the photo-signal processing device passes by the document line. In other words, it is preferred that the distance between the scan start point and the document line is no less than the first constant value.
A second aspect of the present invention is directed to another image scanner. The image scanner includes a scanning platform for placing thereon an object to be scanned, which is marked thereon a document line for positioning a front edge of the object, a first elongated color block located in front of the document line along a specific direction, and a second elongated color block located in front of the document line along the specific direction and having an interface with the first color block; and the image scanner also includes a photo-signal processing device passing by the scanning platform from a home position along the specific direction, and performing a scanning operation from a scan start point behind the first and the second color blocks to read image data of the object, and converting the image data of the object into digital data for further processing. According to this aspect of the present invention, each of the first and the second elongated color blocks has a length greater than a length of the photo-signal processing device so that the photo-signal processing device detects colors of the first and the second elongated color blocks as standard colors for color calibrations when the photo-signal processing device passes by the first and the second elongated color blocks, and wherein the interface of the first and the second color blocks includes a first reference point and a second reference point whose coordinates are detected according to color changes therearound, a shift from the first reference point to the scan start point is of a predetermined vector which can be used together with the coordinate of the first reference point for determining a position of the scan start point, and a distance between the first and the second reference points is of a constant value which can be used together with the coordinates of the first and the second reference points for determining a deflection rate of a scan track and an amplification error of a scan result.
A third aspect of the present invention is directed to a method for improving a scanning quality of an image scanner. The image scanner includes a scanning platform for placing thereon an object to be scanned, and a photo-signal processing device passing by the scanning platform along a specific direction to perform a scanning operation for the object. The method includes steps of providing a document line on the scanning platform for positioning the object; providing a first color block on the scanning platform, which is located in front of the document line along the specific direction; providing a second color block on the scanning platform, which is located in front of the document line along the specific direction and has an interface with the first color block; detecting respective coordinates of a first and a second reference points in the interface of the first and the second color blocks according to color changes around the first and the second reference points when the photo-signal processing device passes by the first and the second color blocks along the specific direction; determining a scan start point according to the coordinate of the first reference point and a predetermined vector indicative of a shift from the first reference point to the scan start point; and determining a deflection rate and/or an amplification error of a scanning result according to the coordinates of the first and the second reference points and a predetermined distance between the first and the second reference points for correction of the scan result.
Preferably, the present method further includes a step of detecting colors of the first and the second color blocks as standard colors for color calibration of the scanning result when the photo-signal processing device passes by the first and the second color blocks along the specific direction.
In a preferred embodiment, the first and the second color blocks are rectangular regions of standard white and standard black, respectively, for performing color calibrations of a light and a dark responses, and the first color block is enclosed within the second color block so that the photo-signal processing device sequentially passes by the standard black region, the standard white region and the standard black region along the specific direction. As for the interface between the first and the second color blocks, the line overlapping either a front edge or a rear edge of the first color block can be indicated as the interface. In this case, the first and the second reference points are two end points of the indicated edge.
In another preferred embodiment, the first and the second color blocks are rectangular regions of standard black and standard white, respectively, for performing color calibrations of a dark and a light responses, and the first color block is enclosed within the second color block so that the photo-signal processing device sequentially passes by the standard white region, the standard black region and the standard white region. As for the interface between the first and the second color blocks, the line overlapping either a front edge or a rear edge of the first color block can be indicated as the interface. In this case, the first and the second reference points are two end points of the indicated edge.
According to the method according to the present invention, the photo-signal processing device moves a predetermined distance from the interface along the specific direction to reach a scan start point where the scanning operation starts to be performed. The pre-determined distance should be adequately selected to have the scan operation start at the moment or before the photo-signal processing device reaches the document line.
When the detected coordinate positions of the first and the second reference points have been determined as (x1,y1) and (x2,y2), respectively, the deflection rate m can be calculated by equation m=(y2xe2x88x92y1)/(x2xe2x88x92x1), and the amplification error xcfx81 can be calculated by equation xcfx81=1xe2x88x92[(x2xe2x88x92x1)2+(y2xe2x88x92y1)2]1/2/L, in which [(x2xe2x88x92x1)2+(y2xe2x88x92y1)2]1/2 indicates a detected length between the two reference points, and L indicates a predetermined distance between the two reference points.